The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Sour gas often contains significant quantities of dissolved elemental sulfur, which tends to precipitate in numerous points during transport, including the well string, the gas gathering system, and in downstream gas treating and gas processing equipment. To avoid such problems, solvents, such as hydrocarbon oils can be injected into the well string or gathering system to solubilize the sulfur into liquid phase and to thereby prevent precipitation of the elemental sulfur. Most commonly, aromatic solvents (e.g., alkyl naphthalene) are used as solvents as they typically exhibit a higher elemental sulfur solubility than paraffinic or naphthenic hydrocarbons. A typical example for such a system is described in U.S. Pat. No. 4,322,307.
All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
For such treatments to be economically feasible the solvents utilized for solubilization of sulfur are frequently regenerated and reused. Regeneration of sulfur laden aromatic hydrocarbon solvents is commonly achieved by contacting the rich solvent with an aqueous solution comprising an amine (e.g., ethylamine). In such systems, the sulfur is converted to a polysulfide and migrates into the aqueous phase, thereby regenerating the hydrocarbon solvent, which is then recycled. The aqueous solution containing the amine and polysulfide/sulfur is then regenerated by distillation to provide an aqueous amine solution as the overhead product and impure, molten elemental sulfur as the bottoms product. For example, U.S. Pat. No. 5,242,672 describes a typical regenerator unit. While such systems generally achieve desirable sulfur reduction in the sour gas, numerous difficulties nevertheless remain. Among other things, regeneration of the solvent using an amine solution requires significant quantities of energy for heating and pumping. Moreover, and depending on the particular sour gas, chemical stability of the amine solution may be less than desirable and require stabilizers and/or replacement of the amine. Also, the polysulfide and/or sulfur obtained from such regeneration may at least in some cases require additional processing to provide a desirable end product.
More recently, solvents utilized for solubilization of elemental sulfur have been regenerated by hydrotreating, as disclosed in U.S. Pat. No. 7,988,767. In this process, hydrocarbon solvents such as naphthenic hydrocarbons, paraffinic hydrocarbons, and aromatic hydrocarbons are treated using a hydrogenation reaction to generate hydrogen sulfide and a regenerated solvent. The hydrogen sulfide product is removed from the regenerated solvent and converted to elemental sulfur (for example, in a Claus unit), while the resulting regenerated solvent is then returned for reuse.
Unfortunately, while recycling reduces the use of solvents the expenses incurred in their purchase are still considerable. Moreover, the solubility of sulfur in such solvents is also often limited, which necessitates increased solvent use, recycling rates, and costs for associated equipment. Thus, there is still a need for economical solvent systems that are useful for elemental sulfur extraction from sour gases and that have improved elemental sulfur solubility.